Articulated stent

ABSTRACT

An articulated stent for delivering through a bodily conduit, for example, a peripheral or coronary artery, which has one or more curved portions and for implantation therein. The articulated stent includes at least two substantially rigid segments and a flexible connector for connecting adjacent segments. The connector assumes a cylindrical configuration when relaxed and a differentially stretched and compressed curved configuration when flexed.

RELATED PATENT APPLICATIONS

This application is a continuation of prior application Ser. No.09/026,750 filed Feb. 20, 1998, (now U.S. Pat. No. 6,059,811) which is acontinuation of Ser. No. 08/760,359 filed Dec. 4, 1996 (now U.S. Pat.No. 5,980,552), which is a continuation of Ser. No. 08/455,462 filed May31, 1995 (abandoned), which is a continuation of Ser. No. 08/213,272filed Mar. 17, 1994 (now U.S. Pat. No. 5,449,373).

FIELD AND BACKGROUND OF THE INVENTION

The present invention relates to stents which are implanted as part of aballoon angioplasty procedure within a bodily conduit of a living animalor a human to maintain patency. In particular, the present inventionrelates to articulated intravascular stents for delivery through orimplantation in a blood vessel having a curved portion.

Intravascular stents having a constricted diameter for delivery througha blood vessel and an expanded diameter for applying a radiallyoutwardly extending force for supporting the blood vessel are known inthe art. Articulated intravascular stents for either delivery through acurved blood vessel or implanted therein are also known in the art.

Self-expandable articulated stents are described, for example, in U.S.Pat. No. 5,104,404 entitled “Articulated Stent” to Wolff. Balloonexpandable articulated stents are commercially available under the tradename Palmaz-Schatz Balloon-Expandable Stents from Johnson & JohnsonIntervention Systems Co.

A prior art self-expandable articulated intravascular stent 10 deployedin a curved blood vessel 16 is now described with reference to FIG. 1which is, in actual fact, FIG. 2 of the above referenced U.S. Pat. No.5,104,404. Stent 10 is made up of a number of individual segments 12articulated by hinges 14 connected at each end to segments 12. Stent 10is preferably fabricated from memory shape material, for example,nitinol, and as such is self expandable after delivery from a deliverysystem described in U.S. Pat. No. 4,830,003 to Wolff et al. However,these prior art articulated intravascular stents suffer from a number ofdisadvantages both during delivery through a curved blood vessel andwhen implanted therein as will now described.

The delivery of stent 10 through curved blood vessel 16 is morecomplicated than the delivery of a non-articulated stent in that stent10 has to be angularly oriented such that its hinges 14 are locatedtowards the convex portion of blood vessel 16 so that stent 10 can beflexed inward. In the present example, it will be noted that hinges 14are located on the same side of segments 12 because blood vessel 16 hasonly a simple curve in one plane. It can be readily appreciated thatdelivery of stents through blood vessels which have one or more curvedportions which are not in the same plane is even more complicated andgenerally requires specially constructed stents.

Even when implanted in a curved blood vessel 16, stents 10 are shown tobe lacking in that the gaps between segments 12 render the curvedportion of blood vessel 16 without support. Furthermore, the gaps at theconvex portion of blood vessel 16 are substantially greater than thegaps at the concave portion thereof, thereby inducing non-uniform andtherefore undesirable stresses on blood vessel 16.

Therefore, it would be highly desirable to have an articulated stentwhich does not require any particular angular orientation when beingdelivered through a curved bodily conduit and provides continuous anduniform support for both straight and curved portions of a bodilyconduit when implanted.

It would also be highly desirable the structure of a stent does notdepend on the particular orientations of curved portions of a bloodvessel.

SUMMARY OF THE INVENTION

The object of the present invention is for an articulated stent whichcan be delivered through a curved bodily conduit using a routine medicalprocedure and a conventional stent delivery system. Furthermore, thestent provides continuous and uniform support for both straight andcurved portions of a bodily conduit when implanted. Still further, thestructure of a stent and its support of a bodily conduit do not dependon the orientations of the curved portions of the conduit.

The objective of the present invention is achieved by an articulatedstent, comprising: (a) at least two substantially rigid segments; and(b) a flexible connector for connecting adjacent segments, wherein theconnector assumes a substantially cylindrical configuration when relaxedand a differentially stretched and compressed curved configuration whenflexed.

After expansion, the rigid segments of the stent preferably present afine diamond shaped mesh having 1 mm long sides to provide continuousand uniform support for straight portions of a bodily conduit.

The connectors can be implemented as a plurality of substantiallyhelical links connecting adjacent segments. Alternatively, theconnectors can be implemented as links each having at least one kink.The connectors typically have between 8-24 links to provide continuousand uniform support for both straight and curved portions of a bodilyconduit.

The stents have constricted diameters for intraluminal delivery and arethen deformed, by the inflation of a balloon forming part of theircatheter delivery system, to expanded diameters for applying radiallyoutwardly extending forces for supporting the lumen of bodily conduits.The constricted and expanded diameters of the stents typically fall inthe ranges of 1.0-3.5 mm and 3.5-10.0 mm, respectively.

The stents are preferably fabricated from low memory, more plastic thanelastic, bio-compatible materials, for example, stainless steel 316L,gold, tantalum, etc. which enables them to be plastically deformed fromtheir constricted diameters to their expanded diameters.

A typical stent for implantation in a human coronary artery is 9-21 mmlong comprising three to seven 2.2 mm long stent segments connected bytwo to six 1 mm long connectors such that the ends of the stent subtendbetween a 45° to 135° angle at a radius of curvature of approximately 9mm when flexed.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is herein described, by way of example only, withreference to the accompanying drawings, wherein:

FIG. 1 shows a close-up view of a prior art articulated stent ofdeployed in a curved blood vessel;

FIGS. 2a and 2 b show a preferred embodiment of an articulated stent,constructed and operative according to the teachings of the presentinvention, in its relaxed and flexed states before plastic deformation;

FIG. 2c shows the expanded stent of FIG. 2 after plastic deformation;

FIG. 2d shows the stent of FIG. 2 mounted on a catheter in its flexedstate;

FIGS. 2e and 2 f show the stent of FIG. 2 before and after expansion bya balloon forming part of its catheter delivery system;

FIGS. 3a and 3 b show a second embodiment of an articulated stent,constructed and operative according to the teachings of the presentinvention, in its relaxed and flexed states before plastic deformation;and

FIG. 3c shows the expanded stent of FIG. 3 after plastic deformation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is of an articulated stent for delivering througha curved bodily conduit, for example, a peripheral or coronary artery ofa living animal or a human and implantation therein as part of a balloonangioplasty procedure to maintain patency.

The principles and operation of the articulated stent of the presentinvention may be better understood with reference to the drawings andthe accompanying description.

Referring now to the drawings, FIGS. 2a-2 c show an articulated stent,generally designated 100, constructed and operative according to theteachings of the present invention, generally comprising a number ofsubstantially rigid segments 102 connected by connectors 110.

Segments 102 are preferably made up to present a fine diamond mesh ofinterconnected diamond shaped cells 108 having 1 mm sides on expansionas best seen in FIG. 2c. Depending on the intended diameter of stent100, segments 102 typically comprise between 8-24 diamond shaped cells108.

Connectors 110 comprise links 112 connecting a front end 104 to a tailend 106 of adjacent segments 102. Links 112 preferably extend in asubstantially helical fashion between apexes of diamond shaped cells 108at front and rear ends 104 and 106 of adjacent segments 102 such thatthe number of links 112 equals the number of cells 108. Links 112 arepreferably evenly deployed around perimeters of segments 102 such thatconnectors 110 can be equally flexed in any direction and to providecontinuous and uniform support to both straight and curved portions of abodily conduit.

Alternate connectors 110 at front and rear ends 104 and 106,respectively, of a segment 102 preferably have links 112 wound inclockwise and counter clockwise directions. Alternately windingconnectors 110 ensures that the rotational displacement of links 112 andadjacent segments 102 relative to the walls of a blood vessel and moreimportantly the balloon of its delivery system is minimized when stent100 is expanded.

It is particular feature of the present invention that connectors 110have a generally cylindrical configuration when stent 100 is relaxed asbest seen in FIG. 2a and a differentially stretched and compressedcurved configuration when stent 100 is flexed as best seen in FIG. 2b.The flexed configuration is brought about by two relatively opposingdisplacements of links 112. First, the differential stretching ofconnectors 110 occurs at the convex portion thereof denoted 114 by links112 being displaced away from one another. Second, the differentialcompressing of connectors 110 occurs at the concave portion thereofdenoted 116 by links 112 being displaced towards one another.

Stent 100 has a constricted diameter for delivery through a curvedbodily conduit as shown in FIGS. 2a and 2 b and an expanded diameter asshown in FIG. 2c for supporting a bodily conduit. Stent 100 ispreferably fabricated from low memory, more plastic than elastic,bio-compatible material, for example, stainless steel 316L, gold,tantalum, etc. which enables it to be plastically deformed from itsconstricted diameter to its expanded diameter. The constricted andexpanded diameters of stent 100 typically fall in the ranges of 1.0-3.5mm and 3.5-10.0 mm, respectively.

With reference now to FIGS. 2d-2 f, stent 100 is shown overlying aballoon 118 forming part of its catheter delivery system 120. Stent 100is mounted on its catheter delivery system 120 in its constricteddiameter state shown in FIG. 2e for plastic deformation throughinflation of balloon 118 to its expanded diameter shown in FIG. 2f forsupporting the walls of a bodily conduit. An exemplary stent forimplantation in a human coronary artery, is typically 15 mm long made upof five 2.2 mm long segments 102 connected by four 1 mm long connectors110 and capable of flexion such that its ends subtend a 90° angle at aradius of curvature of approximately 9 mm.

The delivery of articulated stent 100 is considerably simpler than thedelivery of prior art articulated stent 10 because stent 100 is equallyflexible in all direction and therefore does not require a dedicatedangular orientation to pass a particular curved portion. This advantageis particularly important for delivery through blood vessels havingmultiple curved portions. It is a further advantage of stent 100 overprior art stents 10, that stent 100 provides continuous and uniformsupport along the entire length of a blood vessel by means of segments102 and unflexed connectors 110 supporting straight portions thereofwhile connector portions 114 and 116 supporting convex and concavecurved portions thereof, respectively.

With reference now to FIGS. 3a and 3 b, an articulated stent 122 isshown in which connectors 124 comprise links 126 having one or morekinks 128. The design of connectors 124 is preferred to that ofconnector 110 because stent 100 may have a tendency to rupture balloon118 due to two reasons. First, links 112 overlying the convex portion ofballoon 118 have a tendency to be biased inward when stent 100 isflexed. Second, segments 102 display a rotational displacement relativeto balloon 118 when stent 100 is expanded.

In this case, the differentially stretched and compressed curvedconfiguration of connector 124 is brought about by two relativelyopposing displacements of links 112 as before except that thedifferential stretching of connectors 124 at convex portion 114 occursby kinks 128 being somewhat straightened out while the differentialcompressing of connectors 124 at concave portion 116 occurs by kinks 128being more acutely bent.

In a similar fashion to stent 100, stent 122 has a constricted diameterfor delivery through a curved bodily conduit as shown in FIGS. 3a and 3b and an expanded diameter as shown in FIG. 3c for supporting a bodilyconduit when implanted therein.

While the invention has been described with respect to a limited numberof embodiments, it will be appreciated that many variations,modifications and other applications of the invention may be made.

What is claimed is:
 1. An articulated stent, comprising: (a) at leasttwo substantially rigid segments having, upon expansion, a plurality ofconnected cells each having apices, each of said rigid segmentspresenting a substantially cylindrical structure; and (b) a flexibleconnector, comprising a plurality of flexible links, disposed betweenthe substantially rigid segments, each of the links connecting apices ofadjacent cells on adjacent rigid segments, each of the links, whenviewed laterally, having at least a first portion and a second portionand an area of inflection disposed between the first portion and thesecond portion.
 2. The articulated stent of claim 1, wherein the area ofinflection remains inflected after the expansion of the stent.
 3. Thearticulated stent of claim 1, wherein the first portion and secondportion are of different lengths and wherein the length of the larger ofthe portions is not greater than twice the length of the shorter of theportions.
 4. The articulated stent of claim 1, wherein the area ofinflection enlarges during the expansion of the stent.
 5. Thearticulated stent of claim 1, wherein the first portion and secondportion are substantially straight.
 6. The articulated stent of claim 5,wherein the first portion and second portion are of different lengthsand wherein the length of the larger of the portions is not greater thantwice the length of the shorter of the portions.
 7. The articulatedstent of claim 6, wherein said substantially rigid segments aresubstantially rigid particularly when compared to said flexibleconnectors disposed between the substantially rigid segments.
 8. Thearticulated stent of claim 6, wherein the area of inflection remainsinflected after the expansion of the stent.
 9. The articulated stent ofclaim 6, wherein the area of inflection enlarges during the expansion ofthe stent.
 10. The articulated stent of claim 5, wherein the area ofinflection remains inflected after the expansion of the stent.
 11. Thearticulated stent of claim 5, wherein said substantially rigid segmentsare substantially rigid particularly when compared to said flexibleconnectors disposed between the substantially rigid segments.
 12. Thearticulated stent of claim 5, wherein the area of inflection enlargesduring the expansion of the stent.
 13. The articulated stent of claim 1,wherein the substantially cylindrical structure comprises a mesh. 14.The articulated stent of claim 1, wherein said substantially rigidsegments are substantially rigid particularly when compared to saidflexible connectors disposed between the substantially rigid segments.